MacOS Mojave not able to be installed.

Click on your Desktop Macintosh HD icon and press option+command+i. In that Show info panel, what is the used and available storage figures. You will need a minimum of 20GB of available storage to perform an upgrade, as well as a connected power supply and working Internet connection.

Only full installers are available in the Mac App Store.

Just a thought. Try installing in Safe Mode.

Use safe mode to isolate issues with your Mac - Apple Support

You have not told us anything about your computer. Here are the Mojave requirements: https://support.apple.com/kb/SP777?locale=en_US